Umbra on CFLs and dimmers

Are there compact fluorescent bulbs for lights on dimmer switches? Why can’t I use regular CFLs in dimmers?

Dimly, Julia L. Ottawa, Ontario, Canada

Dearest Julia,

I feel like my brain is squinting when I try to understand electrical current and wiring, but here we go: the short answer is yes, there are now compact fluorescent lamps designed for lights on dimmer switches, and they’re even made by big guys like GE and Philips.

Now you can have your CFL and dim it, too.

Photo: iStockphoto.

The second lesson I will share from the research I did on CFLs is: read the box, and do what it says. If your CFL box says do not use in enclosed fixtures, or use only in upward position, or don’t use outside, follow the instructions. Because — and of course I’m probably the only one who hadn’t realized this — the danger is not that the CFL won’t work. The danger is fire. I just didn’t think those nice, cool-to-the-touch lamps could get it together to make a fire. I’m not so smart sometimes.

You may have noticed my new jargon — lamps — and felt confused. Out (up?) there in the fluorescent-lighting world, what you and I would call “bulbs” have two components. The lamp is the bulby part. It is a pressure-, filament-, and gas-filled tube encased by phosphor-coated glass. When electricity hits the filament, it heats the gas atoms, they whir around and emit UV light, and the phosphor picks up the UV light and starts to glow. That’s why CFLs basically look like intestine-y reformations of fluorescent tubes: the phosphored surface area is key to light production. The chunky base of CFLs contains an integral “ballast,” which regulates the flow of electricity into the lamp (in commercial fluorescents, the ballast can be separated and replaced). The ballast gives the lamp electricity in little spurts, a sort of on-off cycle that prevents lamp blowout. So sometimes — for tiny bits of seconds — the lamp is off and the atoms are not receiving electricity, but the phosphor retains its glow, so we don’t usually notice.

The warnings about using regular CFLs in dimmers (and enclosed fixtures) are related to the efficacy of the ballast. Dimmers work by breaking up the amount of electricity reaching the light fixture. The alternating current within our homes can be conceptualized as a sine wave of electrical current; dimmers reduce the electricity headed to the fixture by blocking bits of it. As you dim the lights, more and more of the sine wave is voided, and the bulbs receive less power.

Incandescent fixtures, which produce light by heating a filament, can make bulbs dimmer as less heat is produced by the filament. But to my understanding, dimmers just don’t work well with regular CFLs. That’s because light from regular CFLs is produced not by heat that can be turned down, but by regulating power to and through a complex gassy tube. First the CFL would dim, but then it would go out altogether, and if you kept trying to use it in the fixture the ballast and the lamp would eventually malfunction.

Happily, companies are now making CFLs that do work in regular household dimmers, with a ballast that has been tailored for the purpose.